1. Field of the Invention
The present invention relates to a dielectric material that can be baked at low temperatures for a short period of time, and a condenser made from the dielectric material, thereby having excellent temperature characteristics, such as a dielectric constant varying within 10% of the base value measured at 20.degree. C. in the temperature range of -25.degree. C. to 85.degree. C.
2. Description of the Prior Art
Ceramic condensers are comprised of a dielectric material and electrodes placed on both sides of the dielectric material. The dielectric material requires, as one of electric properties the temperature dependence of its dielectric constant which is defined by JIS, etc. Examples of the dielectric materials having excellent temperature characteristics of dielectric constant include barium titanate materials which are used for conventional ceramic condensers.
These dielectric materials are usually baked in the manufacturing process of the ceramic condenser. However, the barium titanate materials should be baked at high temperatures of approximately 1300.degree. C in the atmosphere. Electrode materials that can be used at such high temperatures during the baking process include only noble metals which have relatively high melting points, for example platinum, palladium, etc. The use of these expensive noble metals leads to the increase of the ceramic condenser prices.
In order to obtain inexpensive ceramic condensers, the development of dielectric materials having lower baking temperatures and replacing barium titanium have been demanded. The proposed dielectric materials are ones made of perovskite type materials containing lead ion as a base, which have not only low baking temperatures, but provide excellent temperature characteristics of dielectric constant. Since these dielectric materials are sintered at these low temperatures, less expensive electrode materials having lower melting points, e.g., silver-palladium alloy can be used. Therefore, using these dielectric materials, and the electrode materials, ceramic condensers can be made at a lower cost.
With the recent development of compact and very reliable electronic devices, a thick-film condenser has been demanded as a ceramic condenser instead of a conventional chip condenser as the number of circuits placed on a single plate is increased. The thick-film condenser structurally requires a dielectric material that can be baked not only at low temperatures, but for a short period of time. Therefore, a dielectric material that can be used for such a thick-film condenser with flat temperature characteristics will be increasingly required.
However, the aforementioned perovskite type dielectric material must be sintered in an atmosphere of low partial oxygen pressure so as to avoid oxidation and also be maintained at a temperature of 1000.degree. C. or higher for several hours so as to obtain a solid sintered body with a high dielectric constant. When a thick-film condenser is manufactured using the above proposed materials, the dielectric material cannot be sufficiently sintered because a low-temperature and short-time sintering process is required for a thickfilm condenser, thus failing in obtaining a desired characteristic of the condenser. If it is intended to sinter the dielectric material completely, the sintering temperature must be 1000.degree. C. or higher. At such high temperatures, as mentioned above, electrode materials may be oxidized, and therefore, the above-mentioned silver-palladium alloy, or copper that has a further lower melting point, cannot be used, thus preventing the manufacture of ceramic condensers at a lower cost.
The objective of this invention is to provide a dielectric material which has the flat temperature characteristics of dielectric constant and is able to be sintered at a low temperature of 1000.degree. C. or lower in a short period of time. The another objective of this invention is to provide an inexpensive condenser using such a dielectric material.